In the Inspector window, click on the General fold out to open it, you will see the properties as listed below:
Script: the MonoScript associate with this component, double click to open the script if you want to see what's inside.
Mesh Filter: the Mesh Filter component to assign the mesh to. If null, the terrain will not be rendered but instead stored in the GeneratedMesh property.
Collider: the Mesh Collider component for this terrain. Assign this if you want the player to walk on it. This property is assigned automatically if you use Geometry Painter of Environmental Painter.
Update Immediately: should the terrain update right after Inspector changed? Uncheck this to save some processing power on low end machine.